The use of video cameras to transmit a signal to a particular limited audience at one or more specific locations via coaxial cables, telephone wires, fiber-optic strands, microwave radio systems, or communications satellites, as compared to openly broadcast television intended for the general public. See also: Coaxial cable; Communications cable; Communications satellite; Microwave; Optical communications; Telephone service
The term closed-circuit television (CCTV) is slowly falling into disuse and currently refers primarily to older analog video technology used for such functions as monitoring, surveillance, and process monitoring. These are discussed below in more depth. This older CCTV equipment is based on the analog television standards that have been in widespread use since about 1940 and are also described below. This equipment is being replaced by digital television (DTV) and the widely popular high-definition digital television (HDTV). In addition, DTV, coupled with the spread of the Internet, has now made commonplace the use of web cameras (webcams) and Internet Protocol (IP)–based cameras. These are causing what traditionally has been called CCTV to slowly disappear and be replaced by similar web-based applications. For example, the video teleconferencing systems of the 1990s have been made obsolete by applications such as Skype. See also: Internet; Teleconferencing; Television; Television standards
The normal CCTV display device is a television receiver. Until the early 2000s, most receivers used a cathode-ray tube to produce the visible image, but flat-panel displays using plasma, liquid-crystal display (LCD), or light-emitting diode (LED) technology have become common. See also: Cathode-ray tube; Electronic display; Flat-panel display device; Light-emitting diode; Liquid crystals; Television receiver
Current CCTV applications fall into several areas: surveillance and crime deterrence, remote monitoring of processes or events, traffic monitoring, and transport safety. This is a smaller set of applications than just in 2000.
Surveillance and crime deterrence
Surveillance and crime deterrence is the biggest use of CCTV by far. Typical locations for this technology are apartment houses, banks, parking garages, casinos, military facilities, airports, bus and subway stations, and retail stores. These systems may be designed to function in nearly total darkness to detect suspicious activities. Some countries, such as the United Kingdom, and some cities, such as Chicago, have deployed huge numbers of cameras on their streets (reportedly 1.85 million cameras in the United Kingdom) in the name of crime prevention. Some of these systems are wired and some are wireless. They normally use low-resolution, black-and-white video. In some cases the video is digital or is digitized and is stored; and in other cases the cameras are just deployed and, when a crime or accident is reported, a control-center type of facility can switch to the cameras and receive live, real-time feeds from the scene. Almost all of the types of places mentioned above have a dedicated security person or staff of people who monitor the security cameras. Bank branch offices have cameras, for example, at ATM machines, drive-through stations, and inside the bank, but typically they do not have on-site security people; the video is either recorded locally or transmitted to a central location.
Remote monitoring of processes or events
Many types of closed-circuit television systems produce pictures intended for distant viewing when the environment is not suitable for humans to be present. These images may include those taken from a space probe passing close to a distant planet, or pictures of blast furnaces, nuclear power plants, chemical processing plants, or other industrial operations. At the opposite extreme, the low cost of modern video equipment makes practical the use of small cameras to observe sleeping children at home and to enjoy video images of people far away while chatting with them on the Internet.
Medical and scientific equipment as well as industrial robots often incorporate specialized CCTV systems. Modern CCTV cameras used for remote monitoring are small, sensitive, rugged, relatively inexpensive, and durable, with long service lives. Most modern solid-state designs use charge-coupled imaging devices. Video signals are often recorded on magnetic tape for future use. See also: Charge-coupled devices
Since the late 1990s, there has been a proliferation of CCTV cameras around major cities in the United States that are used for traffic monitoring and reporting. These are used for both monitoring of congestion and detection of accidents. When their use began, these systems were owned by private companies or television stations that used them for their own private use. In recent years, many of the cameras that have been deployed are digital, and their output is put on the Internet (with IP cameras, discussed below). It is thus available to everyone by going to a website such as Trafficland.com, which boasts cameras in 35 states, the District of Columbia, and five foreign countries.
CCTV uses in transport safety applications encompass such things as backup cameras in automobiles, and cameras on trains and subway cars to make sure that people are clear of doors and tracks before the train begins moving. There are similar uses on buses and on amusement park rides. These uses are truly CCTV, as the cameras are typically small, analog, and black-and-white, and the video signal is cabled to the display device or monitor, which is normally very close so that no broadcasting is involved. These systems permit relatively inexpensive two-way video and audio connections between schools and among school systems, enabling great flexibility in system design and utilization.
As mentioned above, closed-circuit television systems utilize equipment that produces signals based on the old broadcasting industry specifications. Until around 2006, the standard television broadcast specifications used in the United States were devised in the 1950s by the National Television Systems Committee (NTSC). NTSC systems display 30 complete television pictures (frames) per second, and each frame is composed of 525 horizontal scanning lines arranged from top to bottom. Between 2006 and 2009, under the direction of the Federal Communications Commission, television broadcasters in the United States abandoned NTSC and switched over to digital standards. See also: Television standards
CCTV systems are not required to use NTSC signals, but many do, mainly for economic reasons. In many applications, normal NTSC-based CCTV equipment is satisfactory. Video cameras, television receivers, videocassette recorders, and accessories were produced in large quantities for NTSC broadcast applications and had become quite inexpensive.
When the United States switched to digital standards, the pictures went from 525 lines to the equivalent of 720 lines and also to 1080 lines. This switch is taking place worldwide, and the new broadcast-quality digital equipment, which was very costly initially, is gradually coming down in price. The digital technology, however, also has a low-cost aspect, which has developed very small, low-cost cameras. These are so small that they are routinely built into laptop computers or are sold separately as web cameras to use on the Internet. Sometimes these are called IP (for Internet Protocol) cameras, as they are used to transmit video across the Internet. In fact, such cameras are now available in “smart phones” such as the iPhone, which are gradually incorporating almost all of the capabilities of laptops. These cameras are used to make video calls, using services such as Skype, as mentioned above, and they also can be used for surveillance, all over the Internet. For example, small wireless IP cameras are sold that can connect to the Internet at one's home via a wireless router. This can allow a person at the office to go online and see what that camera at his home is viewing. There have been newspaper stories of people secretly checking on their nannies, spouses, and mistresses in this manner.
One could argue that this is really CCTV in a different form. The argument is stronger when the camera is used in a video-call type of application, as it is really point-to-point; on the other hand, however, the cameras on each end are not dedicated to a particular link, because a call can also be made to a different person. The surveillance camera at a person's house is actually available to anybody with the Internet address and a little bit of networking knowledge. Regardless, the terminology has changed completely, so while the functionality is the same or at least very similar, it is known these days as something entirely different.
As time goes on, technology will permit higher and higher video resolution on larger and larger screen sizes. Even today, resolution is such that, with moderate screen sizes, picture quality approaches that of film. Because the transmission standards were fixed in the 2000s, the current trend seems to be toward mass production of affordable receivers with new features and ever-larger screen sizes, getting away from the weighty plasma technology in favor of the LCD and the lighter, newer LED technologies. Before long, the traditional, older, analog closed-circuit technology will disappear completely. At that point, the applications will still exist but will utilize these newer technologies, and more features will become available; the name closed-circuit will go away, and the applications will be called something else.
Several new applications are being developed or refined for which these higher-resolution digital cameras will be the “enabling technology.” In the security field, automatic facial recognition, retina scanning, and fingerprint identification systems have been under development or in trials for years, but have been hampered by low-resolution CCTV cameras. As both digital imaging techniques and digital memory become smaller and cheaper, these applications will be used more frequently. Initially they will be used for secure entry into buildings, laboratories, files, databases, and so forth. Later on, they may be used in scenarios to pick out terrorists from crowds by comparing selected facial features from the image to images stored in a database.
Another similar application is called video content analysis. The idea is that a high-resolution digital image is stored in memory and then the camera continually feeds in an image that is overlaid on what is in memory; the system is programmed to alarm on certain kinds of differences or patterns. For example, cameras monitoring garages or corridors that are supposed to be empty at night can cause alarms to be generated if motion is detected in certain areas or if a painting is disturbed on a wall in a museum. Another example is monitoring crowds for suspicious behavior, such as when a person is detected by such a system to be moving in the wrong direction. Linking cameras monitoring a street with “geo-coded” coordinates can aid police in tracking a person through an entire area. Again, these applications are “closed-circuit” but are not called that. Other applications require features such as low-light sensitivity, the ability to respond to infrared or ultraviolet light, or very rugged system components. Industrial standards exist for high-resolution closed-circuit systems. Cameras and monitors are available to meet other specialized requirements.
The Internet coupled with the digital revolution has had a far-reaching effect on the design and application of all video, audio, and computer equipment. High-performance, high-resolution, solid-state camera sensors and the digital processing of video signals, taken together, have extended the applications of closed-circuit television systems. The advanced television systems now entering service make use of the advantages of digital signal processing to provide high-quality images to the home, to the classroom, and to industrial locations. See also: Signal processing